1. Field of the Invention
The present invention relates to the field of power generation using thermoelectric devices.
2. Description of the Related Art
Although it has long been understood that thermoelectric devices can be used to generate power, thermoelectric power generation has been little utilized because the efficiency of present generator design and the power density of such generators are too low.
Historically, solid-state electrical power generating systems are constructed from TE Modules or stand-alone TE elements placed between a source of heat and a heat sink. The parts are designed with no moving parts in the power generator its self. Generally, systems that use hot and cold working fluids as the hot and cold sources employ fans to transport the fluids to the assembly.
In other applications, pressurized air and fuel are combusted within the generator. Still in other applications, such as automotive exhaust waste power converters, heat is transported to the generator by the exhaust system. In these devices, the waste heat is removed either by external fans supplying coolant or by free convection through finned radiators.
In applications such as generators that employ nuclear isotopes as the heat source, individual TE elements are configured to produce electrical power. Each TE element is attached to an isotope heat source on the hot side, and to a waste heat radiator on the cold side. No parts move during operation.
New hetrostructure thermoelectric, quantum tunneling, very thin plated, and deposited thermoelectric materials operate at substantially higher power densities than typical of the previous bulk materials and offer the potential for higher system efficiency.
Successful operation of thermoelectric devices with high power density requires high heat transfer rates both on the cold and hot side of TE Modules. One way to achieve this is through rotary designs that lend themselves to high fluid flow rates, and hence, high thermal power throughput. In one preferred embodiment, rotary systems in which a portion of the heat exchanger acts as fan blades, and thereby contributes to working fluid flow, can reduce power into the fan, simplify system design and reduce size.
Further, the heat transfer rate in many systems can be increased by employing heat pipes, as is well known to the art. Such devices use two-phase (liquid and vapor) flow to transport heat content from one surface to another. Where heat is to be removed at a heat source surface, the fluids"" heat of vaporization is utilized to extract thermal power. The vapor flows to a surface at a lower temperature at the heat sink side where it condenses and thus gives up its heat of vaporization. The condensed fluid returns to the heat source side by capillary action and/or gravity.
Properly designed heat pipes are very efficient and transport large thermal fluxes with very low temperature differential. Some keys to efficient operation are that the liquid return process be efficient and that the entire heat source side be wetted at all times, to make liquid always available to evaporate and carry away thermal power. Similarly, it is important that the cool, sink side does not accumulate liquid since heat pipe working fluids are usually relatively poor thermal conductors. Thus, the sink side should shed liquid efficiently, to maintain effective thermal conductance surface.
In one embodiment, discussed herein, properly oriented heat pipes are combined with rotating heat exchange members, to utilize the centrifugal forces induced by rotation of the heat exchangers to improve performance. Rotary acceleration produced by fans and pumps can be up to several thousand Gs, so that with proper design, the liquid phase can be transported from the heat sink side to the heat source side very efficiently. Designs in which the colder end is closer to the axis of rotation than the hotter end, can exhibit very desirable heat transport properties because the centrifugal forces advantageously increase liquid phase flow when. As a result, such designs have increased power density, and reduced losses.
Finally, power generators that are combined with thermal isolation as described in U.S. patent application Ser. No. 09/844,818, entitled Improved Efficiency Thermoelectrics Utilizing Thermal Isolation can further increase performance.
One aspect described involves a thermoelectric power generator having at least one rotary thermoelectric assembly that has at least one thermoelectric module. The at least one rotary thermoelectric assembly accepts at least one working fluid and converts heat from the working fluid into electricity. Advantageously, the at least one rotary thermoelectric assembly comprises at least one hotter side heat exchanger and at least one cooler side heat exchanger. In one embodiment, the at least one hotter side heat exchanger has at least one hotter side heat pipe in thermal communication with the at least one thermoelectric module and a plurality of heat exchanger fins in thermal communication with the at least one hotter side heat pipe. In one embodiment, the at least one cooler side heat exchanger has at least one cooler side heat pipe in thermal communication with the at least one thermoelectric module and a plurality of heat exchanger fins in thermal communication with the at least one cooler side heat pipe. In one embodiment, the least one working fluid is at least one hotter and at least one cooler working fluid.
Preferably, the heat pipes contain a fluid, and the heat pipes are oriented such that centrifugal force from the rotation of the rotary thermoelectric assembly causes a liquid phase of the fluid to gather in a portion in said heat pipes. For example, the fluid in the cooler side heat pipes is in a liquid phase at at least a portion of an interface to the at least one thermoelectric module, and the fluid in the hotter side heat pipes is in a vapor phase at at least a portion of an interface to the at least one thermoelectric module.
In one embodiment, a motor coupled to the at least one rotary thermoelectric assembly spins the at least one rotary thermoelectric assembly. In another embodiment, the least one working fluid spins the at least one thermoelectric assembly. Preferably, the spinning pumps the working fluid through or across the heat exchangers, or both through and across the beat exchangers.
In one preferred embodiment, the at least one rotary thermoelectric assembly has a plurality of thermoelectric modules, at least some of the thermoelectric modules thermally isolated from at least some other of the thermoelectric modules. In another embodiment, the at least one hotter side heat exchanger has a plurality of portions substantially thermally isolated from other portions of the hotter side heat exchanger.
Another aspect described herein involves a method of generating power with at least one thermoelectric assembly having at least one thermoelectric module. The method involves rotating the at least one thermoelectric assembly, passing at least one first working fluid through and/or past a first side of the at least one thermoelectric assembly to create a temperature gradient across the at least one thermoelectric module to generate electricity, and communicating the electricity from the at least one thermoelectric module. In one embodiment, the method also involves passing at least one second working fluid through and/or past a second side of the at least one thermoelectric assembly. The rotation may be obtained in any number of ways, such as with a motor, with the working fluid itself, and in any other feasible manner to spin the thermoelectric assembly.
Preferably, the at least one thermoelectric assembly has at least one first side heat exchanger and at least one second side heat exchanger, and the step of passing the at least one first working fluid involves passing the at least one first working fluid through and/or past the first and/or second side heat exchanger.
As with the apparatus, in one embodiment, the at least the at least one first side heat exchanger has at least one first side heat pipe in thermal communication with the at least one thermoelectric module and a plurality of heat exchanger fins in thermal communication with the at least one first side heat pipe. Advantageously, the heat pipes contain a fluid and are oriented such that centrifugal force from the rotation of the at least one thermoelectric assembly causes a liquid phase of said fluid to gather in a portion in said heat pipes. The configurations for this method are as with the apparatus.
Another aspect described involves a thermoelectric power generation system having a source of at least one hotter working fluid, a source of at least one cooler working fluid, and at least one rotary thermoelectric assembly having at least one thermoelectric module, wherein the rotary thermoelectric assembly accepts the at least one hotter working fluid and converts heat from the hotter working fluid into electricity. Preferably, the system also has an exhaust for the at least one hotter and the at least one cooler working fluids, and at least one electrical communication system to transfer electricity from the rotary thermoelectric assembly.
In one embodiment, the at least one rotary thermoelectric assembly comprises at least one hotter side heat exchanger and at least one cooler side heat exchanger. As with the previous method and apparatus discussion, in one embodiment, at least the at least one hotter side heat exchanger has at least one hotter side heat pipe in thermal communication with the at least one thermoelectric module and a plurality of heat exchanger fins in thermal communication with the at least one hotter side heat pipe. Similarly, in one embodiment, at least the at least one cooler side heat exchanger may have at least one cooler side heat pipe in thermal communication with the at least one thermoelectric module and a plurality of heat exchanger fins in thermal communication with the at least one cooler side heat pipe. Thermal isolation may also be utilized.
These and other aspects and benefits of the present description will be apparent from the more detailed description of the preferred embodiments below.